The present invention is directed to integrated circuits. More particularly, the invention provides a device and method for voltage regulator with low standby current. Merely by way of example, the invention has been applied to a battery powered system. But it would be recognized that the invention has a much broader range of applicability.
The voltage regulator is widely used and integrated onto an integrated circuit chip. The integrated circuit chip may contain numerous transistors with shrinking size. The decrease in transistor size usually requires lowering the working voltage of the transistors. Hence the power supply voltage for the integrated circuit chip decreases with shrinking transistor size. The integrated circuit chip usually serves as a system component. The system also contains other subsystems whose working voltages may be higher than the working voltage of the transistors. Hence the power supply voltage for the system may be higher than that for the integrated circuit chip. For example, the system power supply equals 5 volts, and the chip power supply equals 3.3 volts. In another example, the system power supply equals 3.3 volts, and the chip power supply equals 1.8 volts.
To provide the chip power supply, the system power supply is usually converted by a voltage regulator. For example, the voltage regulator receives a 5-volt signal and generates a 3.3-volt signal. In another example, the voltage regulator receives a 3.3-volt signal and generates a 1.8-volt signal. FIG. 1 is a simplified diagram for voltage regulator. A voltage regulator 100 includes a reference voltage generator 110, an operational amplifier 120, and a voltage divider 130. The voltage generator 110 generates a reference voltage Vref 112. The Vref 112 is received by the operational amplifier 120. The operational amplifier 120 also receives an system power supply Vsystem 124 and generates an output voltage Vout 122. The Vout 122 is divided by the voltage 130 and the feedback voltage Vfeedback 132 is received by the operational amplifier. The Vout 122 is used as the chip power supply. For example, the system power supply is 5 volts, and the desired chip power supply is 3.3 volts. If the Vref 112 equals 1.25 volts, the voltage divider 130 sets Vfeedback 132 to be equal to (1.25/3.3)Vout. In another example, the Vref 112 equals the desired chip power supply. Then the Vout 122 is used directly as the Vfeedback 132 with the voltage divider 130 removed.
The voltage regulator usually provides the chip power supply when the system is in the active mode or the standby mode. The current of the voltage regulator in the standby mode consumes important energy. For example, the operating current of the voltage regulator ranges from 30 to 200 μA. The energy consumption in the standby mode limits the operation time of battery-powered devices. Further, some battery-powered devices require low standby power consumption and cannot rely on the regulator that consumes significant power in the standby mode. Consequently, these battery-powered devices usually cannot take advantage of the shrinking transistor size.
From the above, it is seen that an improved technique for voltage regulator is desired.